In the molding industry, silicone or fluoropolymer resins or chrome plating are commonly used to coat molds and provide for ease of release of molded parts. U.S. Pat. No. 4,244,912 (Battice) describes a molding process in which mold surfaces are treated with certain curable silicone release compositions in the production of high resiliency polyurethane foam cushions, shoe soles and polyester boat hulls.
An example is provided in U.S. Pat. No. 4,239,879 (Fabris et al.) where molds are coated with fluorocarbon resin, such as polytetrafluoroethylene, in the production of shoe soles and heels, energy absorbing bumpers and other automotive items from polyurethanes. However, with the advent of more intricately textured molding patterns, designs using multiple colors and the preference for matte or roughened surface textures in some industries, such as the shoe industry, conventional PTFE coatings have been found to be less than satisfactory.
Various solutions have been proposed to achieve the desired matte finish: (1) mechanical abrading of the mold surface, (2) mechanical roughening of mold surfaces which have been precoated with a nonstick finish, and (3) addition of solid filler material to nonstick finishes which coat the mold surfaces. These proposed solutions have not produced the desired results. Mold surfaces which are mechanically abraded lose their surface characteristics after repeated use and tend to produce glossy molded parts. Heretofore, fillers such as particles of calcium carbonate have been added to fluoropolymer nonstick finishes and have successfully imparted a matte texture to the molded article; but, have reduced the release properties of the fluoropolymer resin thereby making it necessary to use silicone oils for mold release.
However, silicone oils tend to migrate to the finished product that in turn causes a part such as the outer sole of a shoe difficult to bond to other shoe parts. To reduce this bonding problem, it has been found necessary to wash molded rubber parts in chlorine containing solvents such as trichloroethylene. Environmental and health concerns arise from exposure of employees to both silicone mist and the vapors from the chlorine containing solvents.
The disclosure of the previously identified patents is hereby incorporated by reference.